1. Field of the Invention
This invention relates to rotary machines and particularly to wide channel type seals between the rotating and stationary components of a machine.
2. Description of the Prior Art
Rotary seals are conventionally disposed between the rotating and stationary components of a rotary machine to impede the leakage of a fluid medium therebetween. Labyrinth seals are widely used with gaseous mediums to reduce the kinetic energy of the leakage fluid by throttling and expanding the medium. Labyrinth seals are formed of a sealing surface or land on one component and a restrictive ring on an opposing component wherein the ring projects into close proximity with the land. A plurality of restrictive rings are commonly required in series to effect sufficient energy dissipation.
In gas turbine engines labyrinth seals are typically used to prevent the excessive leakage of air into the bearing compartments and to prevent the excessive leakage of air externally of the working medium flow path from one engine stage to another. One construction for sealing between adjacent stages in the turbine section of an engine is shown in U.S. Pat. No. 3,514,112 to Pettengill entitled "Reduced Clearance Seal Construction". A plurality of restrictive rings in Pettengill project toward corresponding sealing surfaces. A throttle aperture is formed between each ring and its corresponding sealing surface. An expansion chamber is formed between each pair of adjacent rings. Air leaking through the first throttle aperture flows through the downstream chambers and apertures establishing a stable pressure differential across each ring of the labyrinth.
Labyrinth sealing is an effective technique for impeding the flow of a gaseous medium from a region of higher pressure in a gas turbine engine to a region of lower pressure at moderate clearance levels between relatively rotating components. Where a lesser clearance can be provided a second type of rotary seal, a "wide channel seal", has been found to be more effective than the labyrinth seal at an equivalent clearance. A wide channel seal is formed of two concentric cylindrical lands, one integrally mounted with the rotating component and one integrally mounted with the stationary component. The lands are closely spaced in opposing relationship to restrict the flow of the fluid medium between the two components by imposing frictional flow losses on the medium. One of the lands conventionally is covered with a honeycomb material to greatly increase flow turbulence within the channel.
Wide channel seals are less costly to manufacture and offer a weight saving when compared to labyrinth seals. Significant technical effort is being directed, therefore, to extending the clearance range of effective wide channel seals to make such seals suitable for use in engines requiring seal clearances of varied dimensions.